The present invention relates to a method of orienting a liquid crystal polymer and, more in particular, it relates to a method of manufacturing a liquid crystal polymer having a light controlling function, which can be used suitably, for example, in the field of opto-electronics.
When liquid crystal material is utilized as a device, it is generally necessary to arrange liquid crystals in a predetermined arrangement (orientation) and such molecular orientation varies depending on external effects such as electric field, magnetic field, shearing force or interface. Application use of the liquid crystal materials to various kinds of optoelectronics has been developed by utilizing the light-controlling function derived from such change of orientation.
Liquid crystals are generally classified into those of high molecular and low molecular materials. High molecular (polymeric) liquid crystals have a feature in which by fixing the oriented state of liquid crystals, the polymeric liquid crystals in the state of fixing their functions are used and they are applied in a field different from that of low molecular liquid crystals. For example, there can be mentioned application uses to orientation film for low molecular liquid crystals (as disclosed in Japanese Patent Application Laid-Open (KOKAI) 61-42618), non-linear optical device (as disclosed in Japanese Patent Application Laid-Open (KOKAI) 62-201419), circular polarizing filter and notch filter (as disclosed in Japanese Patent Application Laid-Open (KOKAI) 60-191203), optical memory (as disclosed in Japanese Patent Application Laid-Open (KOKAI) 62-66990) and color compensation plate for liquid crystal display. For practical use, it is necessary that a molecular orientation is controlled at a high level. For example, a color compensation plate for a liquid crystal display, more specifically, a color compensation plate for a super twisted nematic (STN) liquid crystal display is disposed between, a liquid crystal cell and a polarization plate of a STN-type liquid crystal display for eliminating coloration due to the birefringence effect inherent to the STN liquid crystal display. The color compensation plate for the liquid crystal display serves to re-arrange elliptically polarized light having elliptic coefficient and azimuth angle which are made different depending on wavelength after passing through the cell into linearly polarized light of uniform azimuth angle again. Such a function can be developed only when the liquid crystal high molecular materials are oriented horizontally at a high degree of regularity and high homogenity in a certain direction.
By the way, a method of controlling the oriented state of low molecular liquid crystals by using an orientation film has already been established, which constitutes a fundamental technique for twisted nematic or STN liquid crystal display. On the other hand, as a method of controlling the oriented state of high molecular (polymeric) liquid crystals, a technique of orienting with higher order parameters than those of the low molecular liquid crystals, for example, a method of applying external force such as shearing stress, or a method of applying external force such as electric field or magnetic field has been known in a certain restricted region for any of nematic, smectic or cholestic liquid crystals. However, there is a drawback in such a method, that the control for orientation over a large area is impossible or the uniaxial orientation within a plane can not be controlled even if horizontal orientation can be conducted. That is, it can not be said that a technique capable of highly controlling the orientation of high molecular (polymeric) liquid crystals and fixing the oriented state has been established.
It has been demanded for providing a method of manufacturing a liquid crystal polymeric thin film which is oriented to a uniform direction within a plane in parallel with the substrate without no division to domains.
As a result of the present inventors' studies for a means capable of accurately controlling the orientation of liquid crystal polymers, it has been found that a liquid crystal polymeric film highly oriented in parallel with the rubbing direction can be obtained by depositing a certain kind of liquid crystal polymer on a plastic substrate applied with a rubbing treatment and further subjecting the obtained liquid crystal polymeric film to a heat-treatment at such a temperature that the liquid crystal polymer exhibits a liquid crystal phase. Based on the finding, the present invention has been attained.